I see your thoughts with some hall way walls. I do see some walls in my home that are at right angles to joists, but are stacked three deep about 4 feet apart. I know that they are all at right angles and I guess that one could take one away or maybe even two.
I have always had a fear of doing what some homeowners want with a wall and having the phone ring at my home asking me to come back because the roof fell in. ha ha
I have been painting in a home where another contractor was in there removing a true load bearing wall between a living room and a dining room. This removal made a huge room, ample space for one of those 54 inch or so TV's.
He was installing several what I would call King posts on the sides of the wall to be removed and then installing a 4 x 12 beam that would traverse the room and serve as the support for the lost load bearing wall.
As you stated, one should always consult with a struct. engineer and a contractor good with beam spans.
The job looks extremely easy its the thought behind the job that must count.
Thanks for your insight and thought provolking post.